Plasma processing often involves direct plasma interaction with a substrate and plasma cleaning often involves interaction between plasma-created radicals and surfaces of a processing chamber. In the processing context plasma is typically created in the processing chamber using high voltages, and thus the plasma is highly energized. High energy ions in the plasma bombard surfaces and materials in the chamber and can cause unwanted etching or unwanted deposition. Also, in some chemical etching applications high ion energies are not desirable. For cleaning purposes, radicals are often formed in a plasma within the processing chamber, but here again the high energy ions may detrimentally etch the processing chamber.
Remote plasma sources, where a plasma is generated in a chamber separate from the processing chamber, can overcome the high ion energy problem. Gas can be passed through the remote plasma and form the radicals that are fed into the processing chamber for cleaning the chamber or for chemical etching. However, the radicals decay en route to the chamber and thus a less-than-ideal mixture and density of radicals reaches the chamber.